CN87106642A

CN87106642A - Be used to improve the digital converter of two-wire transmitter output current

Info

Publication number: CN87106642A
Application number: CN87106642.4A
Authority: CN
Inventors: 约翰·A·基伯; 理查德·L·尼尔森; 截维德·L·彼德森
Original assignee: Rosemount Inc
Current assignee: Rosemount Inc
Priority date: 1986-10-02
Filing date: 1987-09-30
Publication date: 1988-06-22
Also published as: KR880701929A; NO882395D0; IL84004A0; HK135094A; NO300566B1; EP0324784A1; DE3750297D1; IL84004A; EP0324784A4; DK297588D0; KR960014487B1; AU611649B2; AU8039387A; JP2529874B2; DE3750297T2; ATE109295T1; WO1988002528A1; NO882395L; CA1334994C; EP0324784B1

Abstract

Comprising a sensing assembly, mimic channel, with one to two-wire loop provide a representative by the existing simulated dual line sensor of the process variable of sensitivity (for example pressure) in, with comprise one digitally the equipment of the digitalizer of calculating sensor output replaced analogue detection circuitry.Improved this output by calculating linearity correction.Analog driver circuits also can replace with replacing exciting circuit, and the exciting circuit and the digitalizer of replacement are energized in proper order, with the control exciting current.A charge pump can be coupled to the electric current of loop with the balance series circuit.Digitalizer goes out to provide electrical separation and zero-bit adjustment.

Description

The present invention relates to digital converter.This converter can improve the output current of the two-wire transmitter of sensitive procedures variable.

Existing analog two-wire transmitter comprises a kind of sensor assembly apparatus relevant with process variable.This device is used for sensitivity and sensitive element output signal as the process variable function is provided.Existing sensor also include be connected with the sensor assembly apparatus and provide the exciting bank of excitation to it.Existing sensor comprises analoging detecting device.This pick-up unit is used for exporting the analog-converted that sensitive signal is provided to representing by the two-wire transmitter of responsive process variable.Through the sensor that the present invention has improved, its output obtained good improvement.From sensor, remove the analog detection apparatus, and replaced the replacement equipment of the sensor output of having disposed digital computation.This replacement equipment receives the output of sensitive element, and provides linear or other corrected value to this output.In a most preferred embodiment, removed existing exciting bank, this equipment then include be configured in the sensor and with the replacement exciting bank that is used for providing the sensing assembly device of excitation to be connected to it.In other most preferred embodiment, it is the capacitive character sensitive element of a sensitive procedures variable at least that the sensor assembly apparatus includes, comprise the means for correcting that output is joined with sensitive element, in order to providing correcting value, and comprise in order to the analog correction device of analog correction amount to be provided to sensitive element to it.

In the another one most preferred embodiment, this equipment also comprises one with giving the microprocessor that calculates output calibration value, interval and carry out the zero-bit adjustment.When sensor was still stayed the original place and follow process variable and loop to join, existing sensor output was improved like this.So need not replace existing sensor assembly or make sensor and production line or two-wire circuit are separated, the sensor of the output of figure adjustment just can be provided.

Fig. 1 is the analog sensor of prior art.It is the cut-open view that the top frame and the bottom frame of part have been removed in a demonstration.

Fig. 2 is a sensor of the present invention.It is the cut-open view that the top frame and the bottom frame of part have been removed in a demonstration.

Fig. 3 is the calcspar of first embodiment of sensor of the present invention.

Fig. 4 is the calcspar of sensor second embodiment of the present invention.

Fig. 5 A, 5B and 5C have provided sensor line figure of the present invention together.

Among Fig. 1, the process variable sensor of prior art is with 10 expressions.With bolt sensor 10 and ring flange unitor 12 are linked.12 then are connected to fluid in the sensor 10.The pressure of fluid on the sensor 10 responsive ring flange unitors 12 provides an output current of representing the responsive pressure that arrives for simultaneously two-wire circuit 14.Sensor 10 is by the external power source 14A power supply that is connected in the two-wire circuit, and output current provides a for example output of 4～20 milliamperes for the external loading 14B that is connected in the two-wire circuit 14 simultaneously.Sensor 10 contains a housing 16.Housing 16 has three

cabins

18,22 and 24 of sealing each other.Sensor 10 also comprises a capacitive character pressure-sensing device 26 that is configured in the cabin 18.Sensitive element 26 is used for responsive to pressure reduction, and gauge pressure or absolute pressure be some process variable like this.Sensitive element 26 is connected on the circuit connection board component 28 in the cabin 18 by two leads.Terminal block assembly 28 comprises the diode 30 that the sensitive element output current is carried out rectification, also comprises the analog quantity correcting element 32 that is used for proofreading and correct sensitive element output.Described correction comprises temperature compensation.Cable 34 couples together the terminal block 38 in circuit connection 28 and the cabin 22 by an O-ring seal 36 between cabin 18 and 22.For providing sensitive element 26 characteristics required temperature compensation, unitor plate 38 also comprises additional analog quantity corrector compensating circuit 40.For connecting sensor circuit, terminal block 38 is furnished with a multioutlet joint 42.

When work, sensitive element 26, circuit board assemblies 28, cable 34 and electric wire connecting junction plate 38 have constituted the sensor assembly 35 in the sensor 10 together.At this moment, sensor assembly 35 sensitive procedures variablees provide a sensitive element output signal that contains the compensation of temperature simulation amount also for unitor 42.

Lug plate 44 in pressurized capsule 24 provides connection for the two-wire circuit in the conduit 14C 14.Lug plate 44 have with two-wire circuit from the cabin 24 feeder equipments 46 that are connected to the sealing in cabin 22.Put into an analog converter and exciting circuit assembly 23 in the cabin 22 in housing 16.Exciting circuit assembly 23 utilizes mimic channel to encourage sensitive element, simultaneously the conversion of signals of sensitive element is become 4～20 milliamperes output current.Assembly 23 comprises printed circuit board (PCB) 23A and 23B.23A comprises analog quantity converter and the excited electrons equipment that is connected with multioutlet joint 42; 23B comprises interval and the zero-bit adjustment circuit that is connected with 23A.Screw 50 is adjusted in a pair of sealing, and 22 inside surface extends to the outside surface of sensor housing 16 from the cabin.By adjusting screw 50, can adjust interval potentiometer 23C and zero-bit potentiometer 23D on the printed circuit board (PCB) 23B.Analog quantity converter provides reliable, the low-cost device that produces output signal.Utilize potentiometer 23C, 23D can finish setting of interval and zero-bit.Mechanical adjustment potentiometer 23C, 23D may be subjected to the influence of mechanical vibration, because the position that mechanical vibration might change at interval and zero-bit sets.Potentiometer 23C, 23D can adjust to the interval of output signal and the position that sets of zero-bit on all resolving powers and calibration of potentiometer.Analog correction circuit in the sensor has then improved the linearity as 4～20 milliampere output signals of the sensor of the function of the responsive pressure of quilt, and work as at analog converter, for this non-linear providing when adjusting, then utilize digital circuit that the linearity of output current is further improved in excitation or the sensor assembly.

Investment at process plant's assembling or sensor installation 10 is appreciable.Sensor 10 if dismantle, and with the higher sensor of a kind of precision, for example use the sort of sensor of digital circuit to replace, and so, whole erected costs of the sensor 10 all just have been wasted.When in process plant, such as in chemistry, oil or ore pulp and the paper mill under the situation of sensor installation 10, fully more emat sensor 10 will be the time-consuming again thing of cost money.Connecing in the pressure piping of ring flange unitor 12, if there is not independent cutting-off valve, then have at least a part of factory to stop work, so that line pressure is reduced, make that working fluid is unlikely from ring flange unitor 12 and overflows when sensor unloads ring flange unitor 12.If cutting-off valve is arranged, then in the time of emat sensor more, then need they whole cut-outs.Ring flange unitor 12 need unload from sensor 10, will use bolt again to the sensor of changing simultaneously.For the sensor of changing, when with bolt flange dish fishplate bar 12 time, because have leakage, so need to check sealing gasket between two flange plates unitors 12.More behind the emat sensor 10, when considering more emat sensor, air can enter the force feed pipeline, thereby the sensor after changing usually needs to make its force feed pipeline deaeration.Finish the replacing of sensor 10, the joint in loop 14 and the sensor 10 44 need be disconnected, also conduit 14C and sensor 10 will be disconnected simultaneously.Next step will reconnect to the sensor of changing among loop 14 and the conduit 14a and go.Sometimes, it is not practicable closing process plant for emat sensor more, in the time of can only waiting factory repair just routine close.Consider that the conduit that is connected with ring flange unitor 12 and conduit 14C may be because aging, corrosion and vibration and attenuation, so, when changing whole sensor, may damage some parts in operating process.If not whole replacing, just replace analog electronic equipment in the sensor 10 with digital quantizer, whole replacement cost had both been saved in then this improvement, had saved the time again.When adopting digital quantizer, be unlikely the production that hinders factory self on the one hand, another side also is unlikely and hinders pressure piping, flange unitor 12, return line 14, lug plate 44 and the conduit 14C that leads to sensor.And digital converter can provide electrical separation and zero-bit adjustment; Thereby avoid using the pot that is sensitive to vibration.Can finish at interval and the electric adjustment of zero-bit by the resolving power higher again than pot resolving power.Simultaneously, also provide more accurate interval and zero-bit to set the position.Digital converter but also can comprise digital linear compensation.The compensation of this digital linear provides at the better sensor output signal of internal linear in a big way.The major part of sensor 10 such as housing and sensor assembly comprise the web member of temperature compensation component, lug plate and link circuit, all applicable to digital circuit, simultaneously, are high-precision with the improvement in performance of sensor.Therefore, analog converter can be removed from sensor, and replaces with digital converter, and making becomes desired level by the sensor improvement of being equipped with digital converter.Sensor after the improvement avoided causing in the investment of aspects such as starting material, the compensation of assembling labour, analog quantity and production line installation in the waste aspect raw material and the labour.At interval, zero-bit and other adjustment all can be finished by digital quantizer, and need not use pot, and thereby obtained high stability and polarization.

Fig. 2 is an exemplary sensor 11.This sensor comprises an above-mentioned digital converter.Among Fig. 2, its reference number has corresponding performance with identical parts among Fig. 1.Parts 23 are removed from sensor 11.Sensor 11 is delivered to loop 14 with its output signal.This output signal has improved precision, it by the loop again with a control system interfaces.Except that the compensation of sensor analog quantity that assembly is done, converter 52 also provides second to proofread and correct or compensation, like this, the output quantity of sensor just is improved to desired level, has but avoided the trouble for changing whole sensor spended time and cost and causing thus.

Converter 52 is installed in the cabin 22 of sensor 11, and is sealed in the sensor the inside.The circuit design of converter 52 becomes and can control energy store, and has so also just kept the intrinsic security performance of sensor.

Fig. 3 is the calcspar of first embodiment of sensor 500 made in accordance with the present invention.Sensor 500 joins with process variable along line 514.Line 514 can comprise absolute pressure, gauge pressure differential pressure, temperature, concentration, flow, electric conductivity, or the like.Process variable on the sensor 500 responsive online 514 simultaneously, produces the output signal as the process variable function.Sensor 500 also comprises output signal joint 502,505.502,504 connect to two-wire circuit 506 along

line

503 and 505 respectively.Driving source 508 is serially connected between the

line

503 and 507 in the loop 506, the energy is provided for simultaneously sensor 500.Sensor 500 also comprises a current controller 536 again.Controller 536 connects to output signal terminals 502 along line 520, also connects to output terminal 504 along line 540 and through resistance 542.Current controller 536 is being controlled conduct in the loop 506 by the electric current I of the process variable function of sensitivity, so electric current I is the function of responsive process variable.So electric current I is exactly a signal of sensor.Electric current I preferably and 4～20 milliamperes electric current of a low frequency that is directly proportional by responsive process variable.Fall in resistance 542 both end voltage for sensitivity, current controller 536 preferably also is connected to output terminal 504 along line 544.Thereby loop current I has been represented in voltage drop.So current controller 536 can the monitoring circuit electric current I, has also constituted the closed-loop control of loop current I.Resistance 510 is connected between the

line

505 and 507 in the loop 506.The loop current I resistance 510 of flowing through is connected with voltage on the resistance 510.Utilize device 512 to utilize the voltage drop of resistance 510.Utilize device 512 can comprise control computer, loop control unit, chart recorder, instrument or other indication, record or opertaing device.

Current controller 536 can produce one first communication output signal.The first communication output signal is (FKS) high frequency, frequency keying serial signal preferably.The keying of the first communication output signal or modulating frequency are preferably selected to such an extent that separate with the frequency of loop current.So, utilize device 512 to work under the big situation about disturbing not having, the first communication output signal can superposition on loop current I and do not disturb the work that utilizes device 512 basically.The first communication output signal comprises the data of the parameter of expression working sensor or installation.These parameters for example have at interval and the zero-bit adjustment, and the series number of sensor is by the knowledge of responsive process variable mark, current amplitude of process variable or the like.The first communication output signal 520,540 connects respectively to output terminal 502,504 from current controller 536 along line.The first communication output signal is also received the line 503,505 in loop 506 respectively from output terminal 502,504.Communication device 516 is received line 503,505 respectively along line 546,548.Communication device 516 is 520,503,546,548,505 and 540 receptions, the first communication output signal from current controller 536 along line.Thereby communication device 516 receives the data that are included in the first communication output signal, and provides above-mentioned data to the operator who is positioned at away from sensor.Communication device 516 preferably is connected with loop 506 capacitives, so that low frequency loop current I is unlikely the communication device 516 of flowing through.When according to Fig. 3 described embodiment send like that with receiving loop on communication signal the time, those those skilled in the art that will appreciate that: this communication signal also can be delivered to sensor by a line or a bus that is separated with the loop.

Also comprised one in the sensor 10 and joined, be used to receive a part of loop current I and with the regulator 518 of the level further stimulus sensor circuit of control with line 520.Regulator 518 will encourage the energy to flow to excitation set 526 along line 522.Also will encourage the energy to be transported to computing equipment 532 along line 524.The part loop current of giving regulator 518 is along being connected to the line 550 between regulator and the line 540 and turning back to the loop along the line 552 between computing equipment 532 and line 540.

Exciting bank 526 produces an excitation output signal.This signal is delivered to sensor assembly 528 along line 527.The sensor assembly is connected with the sensitive procedures variable with process variable along line 514.Excitation output signal on online 527 encourages sensor assembly 528, and sensor assembly 528 then connects by responsive output signal along line 530.This output signal is the function of responsive process variable.Sensor assembly 528 comprises that a sensitive element output signal that is used on line 530 provides the mimic channel 529 of correction.The correction that is provided by mimic channel 529 is used for proofreading and correct from desired sensitive element output signal and has been offset to by the response of the sensitive element output signal of responsive parameter.The compensation that is provided by mimic channel comprises the linearity correction as the responsive output signal of process variable function; Also comprise the temperature compensation of the responsive output signal of expression pressure, flow, electric conductivity, also comprise the cold-weldable compensation of thermocouple, or the like.In an embodiment, sensor assembly 528 also comprises the fairing that is used for the responsive output signal on the rectified line 530.

Responsive output signal on the line 530 is delivered to calculation element 532.Calculation element 532 calculates the output signal of the prediction of a responsive output signal function of conduct.The output signal of prediction is the signal that representative requires output.The signal of this requirement output for example is the amplitude of the electric current I in the loop 506.And the output signal of prediction is the function of sensitive parameter.In calculation element, there is constant 533.Constant 533 representatives are to the figure adjustment of sensor output signal, and this figure adjustment has surpassed the correcting value that mimic channel can provide.Constant 533 can comprise linearity correction, proofreaies and correct the correction of other of the characteristic of zero correction or improvement sensor output signal at interval.Constant 533 includes the multiple correction that linearity, interval and zero-bit are adjusted.The output signal of prediction is delivered to current controller 536 along line 534.In an embodiment, current controller 536 compares actual current I responsive on the output signal and online 544 of the prediction on the line 534 and the Control current on the line 520.So that actual current I is substantially equal to the electric current I by the represented prediction of the output signal of prediction on the line 534.Thereby, adopt analog quantity compensation and digital quantity to compensate the output that improves sensor simultaneously.Because of in sensor 500, having made digital compensation, so represented better by responsive parameter with the electric current that utilizes equipment 512 to be received.

In an embodiment, computing equipment 532 also produces the output signal of expression first a communication output signal.This output signal is delivered to current controller 536 along line 534.Thereby, the current controller 536 first communication output signal on the loop current that superposeed.

In an embodiment, communication device 516 receives the data of expression meter constant there from the operator.Communication device 516 will comprise the second communication output signal of the meter constant on online 546,548.This signal is delivered to line 503,505 respectively.Along line 503,505 second communication signal is delivered to output terminal 502,504 respectively.In sensor 500, the second communication output signal is delivered to calculation element 532 by output terminal 502,504 by resistance 542 and along 522 and 520.Calculation element 522 receives second communication signal, and data are wherein stored as constant 533.So sensor 500 can provide meter constant from afar.And there is no need to place or turn on sensor device 500 is adjusted meter constant 533.Sensor among Fig. 3 has utilized the sensing assembly 528 in the existing sensor.The converter of being changed comprises calculation element 532, current controller 536, regulator 518 and resistance 542.The exciting bank of replacing also can be provided.

The calcspar of second most preferred embodiment of the circuit in the sensor 10 is shown in Fig. 4.4～20 milliamperes of loops 14 in it and two-wire are connected.Sensor 10 is received the loop, join with the

terminals

60,62 in the sensor 10.Driving source, such as accumulator or power supply, connect with the loop load of representing with resistance 66A along line 15.Loop load may comprise such as control computer, chart recorder or reometer.Loop current flows to sensor terminals 60 from power supply 60A, and is flowed out by sensor terminals 62, again along line 62A to resistance 66A.Like this, by in the loop to the sensor 10 supply incentive energy.59 pairs of sensors of diode in the sensor 10 provide the reverse polarity protection.The current amplitude in low frequency loop is controlled by the current controller that joins with terminals 60,62.Like this, the amplitude of loop current is a function of the process variable of sensor sensing.First regulator 68 is connected with terminals 60, and is provided on the line 70 of sensor 10 one first and regulates current potential.Second regulator 72 is received line 70, and on line 74, provide one second to regulate current potential.The electric current of sensor of flowing through is returned to the circuit common wire 76 in the sensor 10, and the common wire links to each other with binding post 62 by resistance 78.The voltage that is added in resistance 78 two ends has been represented the actual current in loop.Pressure drop on the resistance 78 turns back to digital to analog converter (DAC) 82 along line 80, thereby has formed the closed-loop control of current output sensor.The energy is provided for excitation set 84 from line 70,74.At this moment, excitation set produces excitation, and delivers to sensor assembly 88 along line 86.This assembly 88 comprises capacitive pressure-sensing sensing unit, analog quantity linearity and temperature compensation component, also has rectification circuit.

Sensor assembly 88 will as the sensitivity on online 90 to the output signal of sensitive element of function of parameter deliver to integrating circuit 92.In sensing assembly 88, carried out utilizing the temperature compensation of analogue technique.Interface circuit 94 is connected to integrating circuit 92 along

line

91,93, and with integrating circuit and integrating circuit timer 96 and microcomputer 98 interfaces.Integrating circuit is obtained the energy by line 70 and 76.Because the cause of potential difference (PD), interface circuit provide a level deviation, so that guarantee the compatible signal level of receiving.For modulus (AD) converter 99 that forms diclinic rate type, integrating circuit 92, interface circuit 94, integrator timer 96 are worked together with microcomputer.The converter 99 of diclinic rate type is finished from the analog to digital conversion of the compensated analog sensitive element output signal of sensor assembly 88.Dual slope converter 99 is to the digital signal of the output signal of the sensitive element of an expression of microcomputer 98 conveyings temperature compensation.Be low-power consumption and the undersized microcomputer 98 that obtains a standard, so, the microcomputer of single chip preferably chosen.This single-sheet miniature robot calculator is made on the surface-mounted integrated circuit all over, and it includes microprocessor, program storage and random access memory.In another embodiment, if space and power requirement meet design, microcomputer 98 can comprise microprocessor, program ROM and the RAM of separation.In a most preferred embodiment, watchdog timer 102 links to each other with microcomputer 98, and can discover when microprocessor 98 is not finished selected task in the time limit that is set by watchdog timer.Fail to finish the work in the regular hour scope, fault has taken place in this expression microcomputer 98.When this fault took place, watchdog timer resetted microcomputer.The nonvolatile memory 104 that links to each other with microcomputer 98 has been equipped with the constant that representative is used for the digital linear correcting value of sensor.Therefore, through the improved sensor of the present invention, the analog correction that sensor assembly 88 is carried out, return signal of sensor the figure adjustment amount is provided except can be provided at sensor and make the time to signal of sensor.Microcomputer 98 is according to the figure adjustment instruction that is stored in the storer 104, the output of calculating sensor.And its precision of output signal after calculating surpasses the precision of original analog sensor output signal.Sensor output signal after the calculating is delivered to digital-to-analog conversion (DAC) circuit 82 along line 106.DAC82 compares the output signal of prediction signal and expression loop actual current.DAC82 delivers to current controller 66 with a signal along line 108, makes loop current equal the current output sensor of the prediction of requirement like this.Connect communicating circuit 112, the device that receives digital command from the loop is provided to microcomputer 98.Described digital command for example has the penalty constant of sensor, at interval and zero-bit set.Communicating circuit 112 in the sensor connects to the two-way communication circuit that has second communicating circuit 114 along line 126,128,62A, 64A.Second communicating circuit 114 can be the part of digital control system, maybe can be an independent device receiving loop at a distance.Expression interval, zero-bit and linear correction data enter second communicating circuit 114.Second communicating circuit 114 is connected to communicating circuit 112 with a high-frequency signal by the line in return wire 62A, power supply 64 and the sensor 76,126.High-frequency signal is by 112 detections of the communicating circuit in the sensor.Simultaneously, " carrier detection " signal 116 is connected to microcomputer 98 from communicating circuit 112 along line.When perception carrier detection signal, microcomputer 98 is received communicating circuit 112 with the signal on the line 118, thereby connects switch 112 and encourage data set 124 in the communicating circuit 112.Data set 124 carries out both-way communication along line 126,128,76,62A, 64A with second communicating circuit 114.Modulation-demodulation 124 receives meter constant, and is sent to storer 104 through microcomputer.Equally also reception and storage interval and zero correction constant in storer 104.The data that data set 124 will be stored in expression constant state in the storer are sent to second communicating circuit 114.The data that may comprise parameter, sequence number, maintenance resume and the expression process variable of controlling sensor function in the storer 104.

Foregoing circuit can obtain the synthetic energy supply electric current greater than 4 milliamperes of levels of drive from the loop.With exciting circuit 84 and microcomputer 98 series connection,, and realize controlling effectively total loop energy supply exciting current so that identical electric current passes through them.For further reducing the exciting current of loop terminal, between

lead

70,74 and 76, be connected to charge pump.Be the current requirement of two series connection of better balance energy supply circuit, charge pump transmits electric charge between series load.This has just further reduced the energy supply electric current of sensor terminal.In normal operation of sensor, open switch 122, make data set no longer work, thereby further reduced the energy supply requirement.Therefore, the energy supply electric current of being delivered to sensor by loop 14 can remain on below 4 milliamperes so that sensor can be in the loop 14 electric current be 4～20 MAH operate as normal.Yet, carry out the communication following period of time between the two at data set 124 and circuit 114, exciting current consumption may be temporarily above 4 milliamperes.

Fig. 5 A represents the first part sensor line.Among the figure, sensor assembly 88 with dashed lines fence up, and it comprises capacitive pressure-active element 140.Pressure-active element 140 is connected to an array commutation diode 146 by fixed capacity 142,144.Commutation diode 146 is connected to exciting circuit 84.Exciting circuit 84 provides excitation by 146 pairs of capacitive pressure-sensing elements of commutation diode.Sensor assembly 88 also comprises the selected fixed resistance 148,150,152,154,156,158 that is connected together with sensitive element 140 and fixed capacity 142,144 and the thermistor 162,164 of the element by way of compensation that joins with sensitive element 140 and fixed capacity 142,144, so that provide analog temperature compensation for sensitive element 140.Sensing assembly also comprised a corrective capacity 166 that is used for analog quantity converter originally.But for digital quantizer, electric capacity 166 is just of no use, thereby has also suffered with regard to no longer it being connected on this assembly.

Exciting bank 84 comprises resistance 168,170,172,174,176,178, electric capacity 180,182,184,186,188,190,192, amplifier 194,196, transistor 198 and five transformers 200 in order to excitation to be provided that winding is connected together.What introduced with the principle of work of the exciting circuit of the cooperating of sensing assembly with in US patent 3,646,538 is the same substantially.

Sensor assembly 88 will represent that the sensitive element electric current " Is " along the line 202 of sense voltage analog quantity delivers to integrating circuit 92.Sensor assembly 88 also with an analog temperature compensation electric current " It ", is delivered to integrating circuit 92 along line 204.Sensitive element electric current " Is " and temperature-compensated current " It " are containing amplifier 208, and be superimposed on the tie point 206 of the amplifier stage of resistance 210,212,214,216 and electric capacity 218.Form the current potential of expression electric current (Is+It) sum on this amplifier stage online 218, thereby this current potential has been represented the sensitive element output current through the analog compensation circuit correction of sensor assembly.Line 218 is connected to integrator 222 by a switch (field effect transistor) 220.Exist the reference potential of a basic fixed on online 224.This reference potential is connected to integrator 222 by switch (field effect transistor) 226.Integrator 222 comprises the big device 228 of determining, electric capacity 230 and resistance 232, and its connection is shown in Fig. 5 A.Switch 220 and 226 alternating movements are so that make integrator 222 alternately carry out integration to sensitive element voltage and fixed voltage.Output signal on the integrator 222 online 234.This output signal is exactly to being added in the time integral of the voltage on the switch 220,226.Integrator output is delivered to comparer 236 along line 234.Comparer is compared the output voltage of integrator with the actual fixed voltage on the line 238.The output signal of comparer comes out to be connected to Fig. 5 B circuit from line 240, and this sets forth in the back.

Second regulator, 72 a part of supply lines are connected between

lead

70 and 74, and power supply in the middle of forming on online 242 and 238.This second regulator 72 provides reference voltage for the temperature-compensation circuit in exciting circuit, integrator and the sensor assembly 88.The second joint device comprises resistance 244,246,248,250,252, adjustable reference 254 and electric capacity 256,258.Said elements, it connects shown in Fig. 5 A.

The wiring of parts 72 is represented with same mark " J2 " in Fig. 5 B with the wiring that cooperates of other parts shown in " J2 " among Fig. 5 A.

Among Fig. 5 B, non-conjunction 246 and 248 is connected together to be connected to and forms 250 of trigger circuit.The output of comparer (shown in Fig. 5 A) is connected to " set " input end of trigger circuit 250 through wiring J2 along line 240.The first output signal Q of trigger circuit 250 receives shown in switch 226(Fig. 5 A through wiring J2 along line 244) the door input end of switch.The second output signal Q of trigger circuit 250 delivers to shown in switch 220(Fig. 5 A by wiring J2 along line 242) switch the door input end.Driving voltage is connected with each other.A low level timer output signal is provided on the timer 96 online 252 level deviation impact damper 254, impact damper 254 carries the timer output signal of a high level then for transducer 256.It is the timer of CD4536B that timer 96 preferably adopts the piece number of being made by RCA Corp..Transducer 256 carries the high level timer output signal for the RESET input of trigger circuit 250 along line 258.The Q output signal of trigger circuit 250 is received the RESET input of timer 96 through impact damper 260.The Q output signal of trigger circuit 250 is received the input end of microcomputer 98 through transducer 262.The 80C59 that microcomputer 98 is preferably made by OKI semiconductor company.Microcomputer 98 carries a clock signal for timer 96 along line 264.Trigger circuit 250, timer 96 and the integrator 92 common dual slope integrating circuits of forming.The Q output signal of trigger circuit 250 has the pulse width of an expression resultant current (Is+It).Therefore, deliver to microcomputer 98 signal indication by responsive parameter, be included in the analog quantity compensation of being done in the sensor assembly 88.In the width of the pulse signal that comes from transducer 262, microcomputer 98 calculates its time clock, so that finish the analog to digital conversion of sensitive element output current (Is+It).

Watchdog timer 102 comprises transducer 268,270, electric capacity 272,274,276, resistance 278,280, transistor 282 and diode 284.The connection of above-mentioned component is shown in Fig. 5 B.In the time of microcomputer 98 operate as normal, give the watchdog timer transport pulse on the microcomputer 98 online 290 periodically.Pulse on the line 290 resets watchdog timer 102, thereby stops transmitting monitoring timer output signal on online 292.Yet, if microcomputer breaks down, thereby can not be in the time interval of setting by watchdog timer provide a pulse on online 290, watchdog timer output signal on then online 292 is sent, thereby microcomputer 98 is resetted, like this, normal work recovered.

An electrically erasable read-only memory (EEROM) 104 is received microcomputer 98, but and the storage representation digital compensation, at interval and the numeric word of zero-bit.The wiring of EEROM104 also is shown among Fig. 5 B.Microprocessor can be read meter constant that is stored among the EEROM104 and the correcting value that calculates as the output signal of constant function.

For forming a stable clock or time reference, crystal 2 92 is received microcomputer 98.

As for the principle of work of the sensor that has non-volatile storer, then the technology people of this area will appreciate that: a part of RAM in microcomputer 98 can be battery-powered, to obtain non-volatile storage of meter constant etc.

Line

70,74 is linked to each other with level converter with 76, to power to level converter.

Table in Fig. 5 B is connected to circuit in Fig. 5 C with line by microcomputer 98 with the wiring of " J3 ", and

supply lines

70,74,76 is also received circuit among Fig. 5 C by " J3 ".

Adding the connecting line that adds underlined " J3 " among the connecting line of underlined " J3 " and Fig. 5 B among Fig. 5 C joins.

Supply lines

70,74,76 among Fig. 5 C is received circuit among Fig. 5 B by connecting line " J3 ".Sensor connects to loop 14 by the port among Fig. 5 C 60,62.The electric current that comes from the loop enters the port 60 of sensor.Port 60 is connected to line 126 by a polarity protection diode 59.Instrument port 61,63 is connected with diode 59, is shown in Fig. 2 with thinking at lead cabin 24() optional indicating instrument connection is provided.First modulator 68 connects to line 126, so that the excitation of receiving loop electric current partly from the line 126.Regulator 68 is supplied with first voltage that is conditioned to line 70.First regulator comprises resistance 300,302,304,306,308,310,312, electric capacity 314,316,318, amplifier 320, transistor 322,324, diode 326,328, Zener diode 330,332,334,336, and they are linked together as shown in Figure 5, be used for producing and transferred voltage.

Current control circuit 66 is connected between

line

126 and 62 two ends, with the size of control loop electric current.Current control circuit 66 comprises amplifier 350, resistance 78,352,354,356, transistor 358,360, electric capacity 362, Zener diode 364,366.For Control current flows to end 62 from line 126, its connection is shown in Fig. 5 C.Give amplifier 350 inputs a Control current by line 368, and the amplifier output current is transported on the reset transistor 358,360 through resistance 354.Part loop current enters line 76 from line 126 through Zener diode 364, transistor 358,360 and resistance 356.Come from the common ground 76 that the electric current in the operative sensor circuit also enters circuit.In fact, all loop current is delivered to end 62 and is turned back to the loop through resistance by line 76.The voltage at resistance 78 two ends is delivered to DAC82 along line 370.DAC82 is preferably the AD7543 of Analog Devices Inc's manufacturing.DAC82 compares the voltage on the line 370 with receiving the prediction output voltage that comes by DAC from bus 372.Bus 372 is delivered to microcomputer 98(by DAC through wiring " J3 " and is shown in Fig. 5 B).

Communicating circuit 112 is delivered to current controller with the communication output current along line 128, so that provide first communication signal to the loop, as to the explanation that Fig. 3 did.The second communication output signal 126 connects to communicating circuit 112 from loop end 60 along line.Communicating circuit 112 receives second communication signal from line 126, and second communication signal is carried out demodulation.Second communication signal through demodulation is received microcomputer 98(in Fig. 5 B along bus 374 and through wiring " J3 ").Communicating circuit 112 comprises wave filter 376.This wave filter is used for the communication signal that comes self-loop is carried out filtering and amplification.Wave filter 376 is received the detecting circuit 378 that carrier wave is carried out detection.Wave filter 376 is also received the data set 124 that communication signal is carried out modulation and demodulation.Modulation-detuner 124 preferably adopts the TCM3105 by the manufacturing of Tcxas instrument company.Carrier detector 378 is received microcomputer 98(in Fig. 5 B along line 116 and through wiring " J3 ").When detecting carrier wave, on microcomputer 98 is delivered to switch 122 to the data set energy supply with a signal along line 118.

Charge pump 132 is connected between

line

70,74 and 76.Charge pump preferably includes an electric capacity 390 of receiving charge pump integrating circuit 392.Charge pump integrating circuit 392 is preferably by 7660 of Inlensil company manufacturing.Electric capacity 390 is from

line

70,74 chargings, and again toward

line

74,76 discharges, the result makes electric current reach balance then.

So device of the present invention can be installed under the situation of the position that original sensor is placed process plant, and desired figure adjustment amount can be provided.Can avoid changing the required expense of whole sensor, and still can obtain digitally to predict output, so that the linearity correction of numeral to be provided.

The above digital converter of narrating has linear output.Should be realized that; The people that are familiar with this area are used for the present invention non-linear output too, export or are used for reverse action such as square root and export.

Claims

1, a kind of method that second a selected information can be sent to the parameter value sensor, sensor can be by one of them first cover transmission lines, along two-wire current-carrying loop transmission type I information, the current-carrying loop then is suitable for being electrically connected with first and second ends of parameter value sensor, type I information then is made up of the value that the sensor in the parameter value sensor records those, parameter value depends on the situation of the equipment that the parameter value sensor is connected, and the method is characterized in that to comprise:

Disconnect and remove and electrically be connected sensor at first and be affixed to some first cover sensor circuits between first and second end in the parameter value sensor of equipment as described above; With

A second cover transfer circuit that electrically is connected between sensor and first and second end is provided in being fixed on the parameter value sensor of equipment as described above, and the second cover transfer circuit can make the parameter value sensor after the repacking transmit first and second category informations along the two-wire circuit then.

2, the method for claim 1, have the signal that radio-frequency component transmits by utilization in the first frequency scope and transmit the type I information that sends by the parameter value sensor after the repacking, have the transmission signal of radio-frequency component in the second frequency scope that is separated with the first frequency scope by utilization and transmit second category information that sends by the parameter value sensor after the repacking.

3, the process of claim 1 wherein that second transmission lines of parameter value sensor after the repacking can be received in the signal that first and second ends provide, these signals comprise the information that at least temporarily is stored in the there.

4, parameter value sensor, has transfer circuit, transfer circuit is used for along being suitable for and the two-wire circuit that is electrically connected at first and second end of parameter value sensor, the value that transmission is recorded by the sensor in the parameter value sensor of a parameter, parameter value then depends on the situation in the equipment that the parameter value sensor is connected, and the sensor is characterised in that and comprises:

Three end devices that provide there comprise first and second end devices; With

Transfer circuit, transfer circuit comprises a power supply, this power supply can keep different magnitude of voltage on each these end device, described magnitude of voltage is included in first and second magnitudes of voltage on first and second end devices, this power supply keeps tertiary voltage value on the 3rd end device on the intermediate value of first and second magnitudes of voltage, electrically be connected the part between the second and the 3rd end device transfer circuit can by than the transfer circuit that electrically is connected part between the first and the 3rd end device by bigger total current; With

A charging storage facility, it can alternately electrically be connected the first and the 3rd terminal and being connected between the second and the 3rd terminal of continuing.

5, value of consult volume sensor, it has and is used for transmitting the value that sensor records along two-wire circuit transmission by parameter value, the two-wire circuit is applicable to first and second end devices in the value of consult volume sensor and links to each other, parameter value depends on the situation of the equipment that the parameter value sensor is connected, and this sensor comprises:

In transfer circuit, as to offer a value of consult volume sensor microprocessor, the micro processor controls signal to the transmission of first and second end devices and

A resetting means, this device can be worked as parameter value when not being transmitted in the time that is set by the timer that resets, reply the job order in microprocessor.

6, be used to improve the equipment of existing simulated dual line sensor, this equipment has a sensor assembly, a sensor exciting circuit, with a detector circuit that is used for providing the output of the process variable of representing a sensitivity to a two-wire current loop, the said equipment is characterised in that: it comprises a digital component testing circuit, and this detector circuit comprises and being connected between sensor assembly and the current return, be used for the calculation element of the output of calculating sensor digitally and comprise one at current return, be used for providing discernible correction signal to improve the device of sensor output to detector circuit.

7, method that can increase the value of consult volume sensor capability, this sensor is used to receive input information, above-mentioned this sensor has at the very start by cover transmission lines wherein, can transmit output information along a two-wire current-carrying loop, above-mentioned loop is suitable for linking to each other with second end with first end of sensor, output information is made up of by the value that the sensor in the sensor of a parameter records those, parameter value then depends on the situation of the equipment of the sensor that is connected, and said method is characterised in that and comprises:

Disconnect or remove a part of circuit of at least one cover transfer circuit, these circuits be electrically be connected at the very start between sensor and first and second ends in being affixed to the sensor of equipment and

Provide one to overlap transmission and the receiving circuit that electrically is connected between the sensor and first and second ends in being affixed to the sensor of equipment, an above-mentioned cover transmits and receiving circuit can make the sensor of repacking send output information and reception input information.